Rosetta spots first sight of cosmic phenomenon forming in solar system

13 Dec 2018

Artist’s impression of Rosetta descending to the surface of Comet 67P on 30 September 2016. Image: ESA/ATG medialab

Having missed it the first time, ESA scientists have found that Rosetta spotted signs of an infant bow shock around Comet 67P.

Despite its mission ending a few years ago, the European Space Agency’s (ESA) Rosetta spacecraft continues to return major breakthroughs in astronomy.

The space agency has announced that the spacecraft, which had been orbiting Comet 67P, detected signs of an infant bow shock at the comet, the first ever seen forming anywhere in the solar system.

What makes this discovery even more amazing is that the phenomenon wasn’t spotted the first time around; only now with subsequent observations was it made clear to see.

So, what is a bow shock? Similar to the waves carved out of the ocean by the front of a ship, a comet cuts through plasma – the hot, gaseous state of matter comprising charged particles found in the solar system – as solar wind. As the supersonic solar wind flows past objects in its path, such as planets or smaller bodies, it first hits this bow shock boundary.

Bow shocks themselves are not a new phenomenon, having been seen around Halley’s Comet, but also tend to vary in size and shape as plasma interacts with its surrounding environment.

Came as a ‘shock’

During its two-year mission, Rosetta ventured as far out as 1,500km from Comet 67P’s centre to search for a bow shock, but seemingly came away empty-handed.

“We looked for a classical bow shock in the kind of area we’d expect to find one, far away from the comet’s nucleus, but didn’t find any, so we originally reached the conclusion that Rosetta had failed to spot any kind of shock,” said Herbert Gunell, who co-led the latest study.

He added that what the instruments failed to spot was that the bow shock was only in its infancy at the time, something never seen before in the solar system.

“In a new analysis of the data, we eventually spotted it around 50 times closer to the comet’s nucleus than anticipated in the case of 67P. It also moved in ways we didn’t expect, which is why we initially missed it,” Gunell said.

The data would go on to show that when the infant bow shock washed over Rosetta, the comet’s magnetic field became stronger and more turbulent, with bursts of highly energetic charged particles being produced and heated in the region of the shock itself.

Previously, particles had been slower-moving with a weaker solar wind, suggesting that Rosetta might have been ‘upstream’ of a bow shock.

Colm Gorey was a senior journalist with Silicon Republic